Local Exchange Carriers (LECs) within the telecommunication industry implement a variety of digital transmission systems to service their customers. As diagrammatically illustrated in FIG. 1, a typical digital transmission system may contain a first (network or central office site-associated) transceiver unit 10 that is coupled to a first (e.g., central office) end 21 of a single twisted pair of telephone wires (or span) 20, and a second (remote site-associated) transceiver unit 30 coupled to a remote end 22 of the twisted pair 20. Also, the central office transceiver unit 10 may be equipped to supply electrical power over twisted pair 20 to remote transceiver 30.
In such a ‘span-powering’ configuration, it is often desirable for multiple central office transceiver units to provide span power for their respective remote transceiver units from a common or shared electrical power source. For system reliability, a fault-induced transient occurring on any one of the respective twisted pairs powered from the same power source must not be allowed to propagate to the other twisted pair lines, and thereby disrupt the operation of multiple transceivers.
Transceiver disturbance can also occur during an input capacitor charging-current transient, which occurs when a remote transceiver unit is initially connected in an operating system. This type of transceiver disturbance is also not permitted by system reliability requirements.
Once the magnitude of the input voltage being supplied to a remote transceiver unit has increased to a value where nominal operation begins, the remote transceiver unit will present a constant power electrical load to the central office unit power supply. Fault isolation and transient charging current isolation must be compatible with this type of load.